Measurement systems are used in liquid sampling devices, for example. A blood collection device for sampling blood—that is, collecting blood—will be described as an example of a liquid sampling device. Blood collection devices are used in quantitative analysis for nuclear medicine diagnosis (for example, PET (Positron Emission Tomography), SPECT (Single Photon Emission CT), or the like) and, in particular, are used in the measurement of radioactivity concentration in the arterial blood of small animals (for example, mice, rats, or the like).
Specifically, blood is sampled (collected) after a radioactive drug is administered to a small animal, and after plasma separation is performed by means of centrifugation following the completion of the entire blood collection at predetermined time intervals, changes in the radioactivity in whole blood and in plasma over time are measured (for example, see Literatures 1 and 2). More specifically, measurements are performed using an imaging plate (IP) which enables the visualization of radioactive distribution by exposing β+ rays contained in blood. An example of software for obtaining the value of the radiation dose from an IP image obtained from the imaging plate (abbreviated appropriately as “IP”) is Multi Gauge produced by Fuji Photo Film Co., Ltd. With this software, the radiation dose per unit area can be determined by reading the IP image, setting the region of interest using software, and calculating the pixel value in the region of interest.
In Patent Literature 1, after a sample (here, blood) exposed to radiation is placed in a container segmented with prescribed dimensions, the radiation intensity of the sample is measured with an IP, and the area of the sample is measured with a scanner. Since the container is designed with prescribed dimensions, the volume of the sample is determined from the area of the sample reflected in the measurement results. Here, technology is disclosed in which the IP image of the radiation intensity obtained with the IP and the scanner image obtained with the scanner are combined, and the radiation concentration (=radiation intensity/volume) of each sample is calculated. In Patent Literature 2, an example of a container that is segmented with prescribed dimensions is described, and a container in which flow paths into which a plurality of samples are inserted are formed on a planar disc is illustrated.
When determining the radiation concentration in blood, superimposition processing such as that described below is performed. That is, superimposition processing is performed by superimposing an image of a disc imaged by a flat head scanner (scanner image) and a distribution image of β+ rays serving as counting information obtained with an IP (IP image). When this superimposition processing is performed with the software described above, the accurate alignment of the groove (flow path) positions of the disc and the plasma/blood cells can be realized by combining and superimposing the central position of the disc in the image of the disc with the central position of the disc in the β+ ray distribution image.
After the blood is centrifuged, the radiation contained in the plasma-separated plasma and blood cells is separated and counted, so the radiation concentration in plasma can be determined. In this way, the radiation concentration in blood per unit volume can be respectively determined by respectively dividing the radiation intensity of β+ rays of each part by the volume of each part from the counting information of the β+ rays of the portions overlapping the plasma and blood cells separated within the grooves (within the flow paths) on the β+ ray distribution image.